Ladders such as attic ladders are commonly used to provide convenient access to attics of houses or other structures without the loss of floor space occupied by a permanent stairwell. Typically attic ladders are foldable into an inoperative position within a frame contained in the ceiling. In order to minimize the size of this port and the attic space required, the ladder is usually broken into sections which are folded upon one another within the frame and are extended in alignment with each other when the ladder is unfolded for use.
Attic ladders of this type use various types of counterbalancing means to hold the stairs in their inoperative position. Springs are the most common counterbalance means. These springs are attached to a lever arm which has its greatest leverage in the inoperative position. Once the stairway is unfolded, the effective length of lever arm approaches zero as the mechanism rotates.
Previous designs for this mechanism do not allow the lever arm of the spring to become zero and therefore tend to lift the ladder slightly while unfolded. This causes the ladder to feel springy as it is climbed. Also due to different ceiling heights, each ladder must be trimmed to fit a particular installation. Because the ladder does not firmly lock into place, the trimming procedure is very difficult to do correctly.
A further problem with counterbalance mechanisms result from their connection to the ladder. The linkages that connect the counterbalance mechanism to the ladder are stressed when the ladder is loaded. Typically, these linkages are manufactured as inexpensively as possible; though operative, they result in a flimsy feeling ladder.
Attic ladders are connected to the framed opening with a hinge. Typically, one leg of the hinge is attached to the upper section of the ladder and the other leg is attached to the inside surface of the framed opening. This arrangement results in an ineffective energy seal.
A further problem with attic ladders results from the connection between the ladder sections. Typical connections allow the load to be carried by the ends of each rail section. Because of the nature of wood, this causes damage and deformation, which in turn results in increased play in the hinge connection.
An important object of the invention is to provide a hinge which protects the wooden sections of the ladder rails from undue stress.
A further object of the invention is to provide a counterbalance mechanism that offers a firmer and more solid feel.
A further object of the invention is to provide a construction that allows the counterbalance mechanism to remain firmly in an inoperative position while the ladder is unfolded.
A further object of the invention is to provide a hinge construction that improves the energy seal between the frame and the attic ladder door, when the door is closed.